Semiconductor bodies having strained regions are used in MOS transistors, inter alia. FIG. 1a shows, by way of example, a PMOS transistor including a drain region 1, a source region 2 and a channel region 3 in a semiconductor body 4. A gate electrode 5 is arranged above the channel region 3, the gate electrode 5 being separated from the channel region 3 by a gate oxide 6. Both the drain region 1 and the source region 2 are provided with a contact 7 and 8, respectively.
In the example shown the drain region 1 and the source region 2 consist of silicon-germanium, while the channel region 3 is produced from silicon. As a result of the higher lattice constant of silicon-germanium compared with silicon, a compressive strain is produced in the silicon in the plane parallel to the surface in the channel region 3. The arrows symbolize the compressive stress produced. This compressive stress leads to a reduction of the effective mass of the free holes and thus to an increase in the hole mobility.
Another example, illustrated in FIG. 1b, shows the inducing of a tensile stress (represented as arrows) in the channel region 3 by using a suitable covering material 9 above the gate. This induced tensile stress leads to a reduction of the effective mass of the free electrons and thus to an increase in the electron mobility, such that an NMOS-transistor having a lower channel resistance can be produced in this way.
However, the use of different materials for producing the strains has a number of disadvantages. Firstly, it makes the production process more expensive. Furthermore, the use of different materials often also requires an additional material-specific adhesion layer, metallization and passivation materials, such that the production process is more complex and thus made more expensive.